In the medical diagnosis and treatment of various heart ailments, it is highly advantageous for a cardiologist to obtain certain information related to the function and physical condition of the parts of the heart of a patient. The use of nuclear medicine, that is, the administration of a dosage of radioactive material for the purpose of tracing the path or volume of circulatory flow, has for some time been a potential source of such information. This information is typically presented to the attending physician as a radiocardiogram, or RCG, in the form of a tracing by a strip chart recorder. However, existing techniques for obtaining the measurements of cardiac parameters of interest have heretofore involved serious drawbacks. For the most part, such techniques require a catheter to be inserted into the heart or into a vein near the heart of a living patient in order to introduce a bolus of radiopharmaceutical into the heart of the patient under study. The risk of moving a seriously ill heart patient to the catherization laboratory of a hospital and the trauma of inserting a catheter into a vein of the patient has for the most part proven a sufficient deterrent to obtaining the patient data available with an RCG. Furthermore, tradition methods for otaining cardiac dynamic parameters have required insertion of a catheter into the heart followed by injection of dense contrast material and subsequent fluoroscopy. The procedure is time consuming with a certain amount of morbidity associated with the injection of the dense dye material which may cause cardiac arythmias and even change the dynamic parameters of the heart. In addition, the process has heretofore been unduly time consuming since the time required for development of X-rays to precisely locate the patient's heart in order to thereafter obtain meaningful measurements, as is currently the practice, is approximately 45 minutes. Moreover, with existing techniques it has been impossible to obtain all of the required patient data from a single injection of a radioisotope, so that sequential injections of separate dosages of radioisotopes have by necessity been employed. This further lengthens the process of obtaining a RCG. Furthermore, required corrections to one measurement are made on the basis of complementary measurements taken with respect to a different sample of a radioisotope at a different time. Because of inconsistencies in radioisotope injection techniques, heart rate fluctuations, and circulatory variations, the corrected measurements obtained from the RCG may not consistently represent an accurate picture of the various patient cardiac parameters measured.
Despite these various difficulties, there have been attempts to employ various instruments to measure cardiac parameters of patients. One such technique employing a scintillation camera is described in an article authored by Donald Van Dyke, et al, entitled "Cardiac Evaluation from Radioisotope Dynamics," Journal of Nuclear Medicine, Vol. 13, No. 8, pp. 585-592 (1972). This technique was non-invasive in nature, but the results obtained were not of a quality which would provide data of sufficient reliability to form the basis of cardiac diagnosis without the complementary use of invasive techniques. Also, the technique was time consuming in that six hours were required to evaluate all the data for one patient. The count rate proved to be quite low, so that the statistics which provide the basis for the calculations were inherently poor. In this procedure, regions of interest had to be set and results were operatordependent to that extent.
Another technique for obtaining an RCG employing a single crystal scintillation probe is described in an article by Peter P. Steele et al, "Simple and Safe Bedside Method for Serial Measurement of Left Ventricular Ejection Fraction, Cardiac Output, and Pulmonary Blood Volume," British Heart Journal, Vol. 36, pp. 122-133, 1974. This technique requires injection of a bolus of radioactivity by means of a central venous catheter, and is to this extent invasive. In addition, this method requires two sequential injections of doses of the radiopharmaceutical used.
The chamber of greatest interest to cardiologists is the left ventricle, the chamber responsible for supplying blood to the systemic circulation. A probe positioned over the left ventricle provides high frequency data on the left ventricle as well as cardiac output. Since a probe positioned over the left ventricle, by reason of the geometric positioning of the heart chambers within the body, partially views the right heart, pulmonary information can be obtained. However, this viewing of the right heart necessitates a correction for "crosstalk" or background in the analysis of the action of the left ventricle. The derivation of the necessary correction has heretofore not been straightforward. To the contrary, it has been quite complicated and has led to measurements inconsistent with or inconclusive with respect to the techniques employing other conventional instruments. The technique, as practiced by Steele and as described in the aforementioned article in the British Heart Journal, has had fair correlation with contrast angiography, however.